This invention relates to a method and an apparatus for determining quality properties of fish on the basis of light reflection. A fish and a reflection measurement device (5) with a light emitter and a light receiver (6) are positioned in relation to each other, with the light emitter and light receiver of the device directed towards the fish""s inner abdominal wall with peritoneum, so that the light emitter illuminates an area of the fish through the peritoneum and the light receiver captures the light reflected from the fish. The intensity of the reflected light as registered in three or more different wavelength bands in the visible and near-infrared range. The measurement results registered are, after any processing, entered into an algorithm in a calculation unit, where the algorithm express a quality property of the fish on the basis of the reflection of its inner abdominal wall with peritoneum and three or more different wavelength bands in the visible and near-infrared range. The calculation unit automatically calculates the quality property by means of the algorithm and measurement results. The intensities of reflected light are registered in both the visible range, especially between 400 nm and 600 nm and in the near-infrared range, especially between 850 nm and 1050 nm. By means of the method it is possible to measure quality properties of individual fish in a short time in a non-destructive manner, especially the color, Astaxanthin content, and/or fat content of Salmon.
The present invention relates to a method and an apparatus for determining quality properties of fish.
Before farmed salmon is slaughtered in a processing factory, a primary check of meat colour is made. For this purpose ten or so fish are taken from each pond and a piece of fillet cut from behind the vent. An operator compares the colour of the cut fillet in an area near the middle of the fish with the colours on a discrete colour chart containing different colour classes. The results of these test samples are assumed to be representative of the whole pond stock.
Both in production and sales, colour is the most important quality parameter for salmon. Salmon buyers can request information on the colour of a delivered lot in the form of a number corresponding to a colour number or a colour step on the Roche scale, a colour table. Another salmon colour reference is the colour number on the Salmofan scale.
To meet consumer requirements, farmed salmon production is adjusted to give the finished fish the most sought-after colour. The producer can use the content of astaxanthin in the feed to control the colour, as there is a correlation between the administration of this substance and the meat colour of the slaughtered salmon.
The fat content of salmon is another important quality parameter. Buyers dislike fish with too high a fat content. Chemical analysis of fat content is part of production control, but it too has to be carried out by random sampling.
The means currently available for controlling production and supplying customers with salmon of the desired quality are thus relatively crude and labour-intensive.
In EP 0 221 642 (Westinghouse Canada Inc.) a hand-held apparatus is described for grading fish fillets, i.e. cleaned fish cuts. The apparatus illuminates the fillet and measures the strength of the reflected light at defined wavelengths at which haemoglobin exhibits special absorption properties. The apparatus compares the values at different wavelengths with values in a stored data set and assigns to the fillet the colour class with the best match between the values and the data set. Haemoglobin is undesirable in fish fillets as it may lead to more rapid deterioration of the fillets. A quality measure for whitefish fillets measured with this device is that the meat is white.
The above-mentioned methods for measurement of colour require a cutting of the fish to produce a meat surface which can be used for the measurement. As a consequence, the measurement is either destructive or is performed at a relatively late stage of the slaughter process providing few opportunities for controlling the process according to colour of fish meat. Furthermore, currently used methods for determination of salmon quality can only provide one quality parameter each, necessitating several analysis procedures for determining both colour and fat content.
The purpose of the present invention is to provide an objective method for determining quality properties of fish wherein the above mentioned disadvantages are avoided, enabling the quality properties of individual fish to be measured in a short time in a non-destructive method, in particular a method enabling measurement of colour, astaxanthin content and/or fat content of salmon. It is in particular the purpose of the invention to provide a method for determining quality properties of freshly slaughtered fish on a slaughter line or in a grading machine so that each individual fish can at an early stage of processing be graded as to quality properties and subsequently be processed or sold for further processing in accordance with its properties.
The invention is based on the observation that it is possible to determine quality properties of fish, especially meat colour of salmon, by means of light reflectivity of their inner abdominal wall with peritoneum using wavelength bands in the visible and near-infrared range. This is a surprise because the peritoneum of e.g. salmon is mainly opaque to the eye and prevents a subjective evaluation of the colour of the meat lying behind the peritoneum. The ability of the invention to measure meat colour may to a great extend be based on the fact that measurement is performed also in the near-infrared range and that the reflection data thus abtained are used in the algorithm to calculate the properties.
The method of the invention is characterised in that,
a fish and a reflection measurement device with a light emitter and a light receiver are positioned in relation to each other with the light emitter and light receiver of the device directed towards the fish""s inner abdominal wall with peritoneum, so that the light emitter illuminates an area of the fish through the peritoneum and the light receiver captures light reflected from the fish,
the intensity of reflected light is registered in three or more different wavelength bands in the visible and near-infrared range, and
the measurement results registered are, after any processing, entered automatically into an algorithm in a calculation unit, which algorithm expresses a quality property of fish on the basis of the light reflection from the inner abdominal wall with peritoneum, after which the calculation unit automatically calculates the quality property by means of the algorithm and the measurement results.
It is possible to use the method according to the invention for on-line measurement on a slaughter line or in a grading machine for freshly slaughtered fish by using a fully automated equipment and for random sample check at ponds or in processing factories by use of a hand-held instrument.
Advantageous embodiments of the method according to the invention are as follows:
To avoid repeated stoppages on an automated slaughter line or in a grading machine it is an advantage if the measurement can be carried out without interruption, so that the fish continue their movement during the measuring process. One embodiment of the method according to the invention is therefore characterised in that the fish and the light emitter and light receiver of the device are moved in relation to each other in the lengthways direction of the fish during registration of measurement results.
Preferably, a reflection measurement device is used wherein the light receiver is designed to receive light reflected from an area of the fish with a cross dimension of at least 5 mm and at most 25 mm, and the device and the fish is moved in relation to each other so that measurement results are obtained from areas which together form a stripe in the lengthways direction of the fish, with a length of 2.5 to 25 times said cross dimension.
It is an advantage to register several sets of measurement data and especially to register measurement data from different areas of the fish, in order to arrive at a quality property result less affected by noise. Variations in the nature of the meat may thereby be equalized by the calculation of an average and any data for abnormal areas can be eliminated before the property is finally calculated. Preferably, measurement data is registered for different areas of the fish and at least one set of measurement values is used to express the quality property of the fish. Data from different areas may be registered by means of a measurement head which is moved in the lengthways direction of the fish while repeatedly measuring light reflections from new areas of the fish. Another possibility is to use a measuring head with a number of detectors, each covering its own area of the fish. The influence on the measurement of noise and faulty areas can be reduced by the combination or selection of significant measurement values.
Reflection values are preferably registered from different parts of the fish in that the fish is transported past a measurement head and several measurement sequences are recorded, from which one or more may be used in the calculation of the quality property. This simplifies the design of the measurement head. One embodiment is therefore characterised in that the registration is repeated several times, that the fish and the light emitter and light receiver of the device are moved in relation to each other between two measurement sequences, and that at least one set of data resulting from the registrations is entered into the algorithm.
The fish may be cut open in the abdomen and eviscerated before the measurement head of the device and the fish are positioned in relation to each other, by which positioning the measurement head preferably is placed in contact with the peritoneum of the inner abdominal wall of the fish.
Preferably, the intensity of reflected light is registered in the visible and near-infrared range between 400 and 1100 nm. The intensity of reflected light may be registered both in the visible range, preferably between 400 and 600 nm, and in the near-infrared range, preferably between 850 and 1050 nm.
The light emitter may illuminate an area of the fish with broad-spectrum light in the visible and near-infrared range. Division of the reflected light into the different wavelength ranges is then carried out by filtering or spectral dispersion of the light.
The registered measurement results can advantageously be used to determine two or more quality properties, such as colour and fat content. One embodiment of the method according to the invention is therefore characterised in that measurement results registered are entered into an algorithm expressing another quality property of fish, after which the calculation unit automatically calculates this quality property by means of the algorithm and the measurement results. This may be a different algorithm from what is used to determine the first property, but a single algorithm developed to calculate two property values from the same set of measurement data may also be used.
The term xe2x80x9cproperty valuesxe2x80x9d does not necessarily designate a number, such as a step on a colour scale or a percentage fat content. A property or property values may be expressed by a category name, such as dark, normal or light colour, or fatty, normal or lean meat. Combinations of different properties, e.g. colour and fat content, may also express a value. If a buyer has a preference for normally coloured meat containing little fat, the property may simply consist of approval or rejection of the meat for that customer.
In particular it is preferred that quality properties are determined on-line on a slaughter line or in a fish-grading machine and that the fish is conveyed into, through and out of a reflection measurement device mounted on the slaughter line or in the grading machine.
The apparatus according to the invention for determining quality properties of fish is characterised in that it comprises:
a reflection measurement device with a light emitter and a light receiver and arrangements to assist in the positioning of the device and the fish in relation to each other, the light emitter and light receiver of the device being directed towards the inner abdominal wall with peritoneum of the fish, so that the light emitter illuminates an area of the fish through the peritoneum and the light receiver captures light reflected from the fish,
registration means connected to the light receiver of the reflection measurement device, which means are designed to register the intensity of reflected light in three or more different wavelength bands in the visible and near-infrared range, and
a calculation unit with an algorithm expressing a quality property of a fish from the light reflection of the inner abdominal wall with peritoneum in three or more different wavelength bands in the visible and near-infrared range, the unit being arranged to enter measurement results automatically, after possible processing, into the algorithm and to calculate the quality property automatically by means of the algorithm and the measurement results.
Advantageous embodiments of the device according to the invention are as follows:
The apparatus may comprise a conveyor arranged to move the fish and the light emitter and light receiver of the device in relation to each other in the lengthways direction of the fish during registration of measurement results.
The apparatus may also comprise means for registering the intensity of reflected light in different areas of the fish,
In particular, the apparatus may comprise means for repeating the registration several times and a conveyor arranged to move the fish and the light emitter and light receiver of the device in relation to each other between two measuring sequences.
The light emitter may be of such nature that it emits broad-spectrum light in the visible and near-infrared range.
The calculation unit may contain an algorithm expressing another quality property of fish and the calculation unit may be arranged to enter the measurement results in the algorithm and automatically calculate this quality property by means of the algorithm and the measurement results.
In a preferred embodiment the apparatus is arranged to register the intensity of reflected light in the visible and near-infrared range between 400 and 1100 nm. It may be arranged to register the intensity of reflected light both in the visible range, preferably between 400 and 600 nm, and in the near-infrared range, preferably between 850 and 1050 nm.
The apparatus according to the invention may be arranged to register the intensity of reflected light in wavelength bands centred on one or more the following wavelengths: 400 422, 440, 472, 500, 546, 578, 600, 688, 814, 920, 978 nm. At these wavelengths there is a particularly clear correlation between the intensity of reflected light and significant quality properties such as colour, fat content and astaxanthin content.
When the light emitter has a broad spectrum, the light receiver will preferably comprise a spectrophotometer, able to measure the light intensity in the different wavelength bands. This may be a conventional spectrophotometer, which by means of prism or grating divides the light into a spectrum, thus permitting individual or preferred wavelength ranges to be examined by one or more light-sensitive detectors in order to give a measurement for light intensity in different wavelength bands.
In another embodiment of the apparatus the light receiver comprises at least one detector and more than three filters, permitting light in specified wavelength bands in the visible and near-infrared range to pass through, the filters being placed in the optical paths between the light emitter and the detectors. This could be described as a spectrophotometer in a less conventional sense, where different filters are interposed in the light path between the meat and the detector(s). This may provide a more robust design for the photometer. Alternatively the filters may be interposed in the light path between a wide-spectrum light emitter and the meat.
The calculation unit will advantageously comprise an algorithm for determining at least one of the following quality properties: colour, astaxanthin content and fat content, since these properties are of particular interest.
The calculation unit may comprise an algorithm which assigns individual fish a quality class corresponding to the quality property, thus allowing the fish to be sorted or processed according to category.
The device may with particular advantage be arranged at a conveyor for individual transport of the fish to measure the fish singly during transport, in particular freshly slaughtered fish with intact peritoneum. The apparatus according to the invention therefore preferably comprises a conveyor for individual transport of abdominal opened fish with intact peritoneum and scales, and a measurement system for on-line measurement of the fish conveyed.
The calculation unit may comprise an algorithm for detecting faulty areas, the algorithm being arranged to disregard measurement results which deviate significantly from other measurement results from the same or other fish. Only the non-deviating measurement results are used for determining the quality property.
In particular it is preferred that the apparatus according to the invention is designed to perform on-line determination of quality properties of fish on a slaughter line or in a fish grading machine, whereby a conveyor individually conveys fish with cut opened abdomen into, through and out of the reflection measurement device which is placed on the slaughter line or in the grading machine.
Preferably, a non-image-forming light receiver is used, as this allows light to be registered in many wavelength bands, thus giving higher certainty in determining the quality property. For example, a spectrophotometer may be used. The light receiver will preferably be able to register light in bandwidths from 2 to 100 nm. The light receiver may be arranged to receive and register reflected light in 6 to 30, or preferably 8 to 20 different wavelength bands in the visible and near-infrared range. This total of xe2x80x9cchannelsxe2x80x9d is sufficient for precise determination of the quality property.
In the present invention, the term fish shall particularly be understood as salmon, but may also be applied to trout, tuna and other fish with high quality requirements.